1. Field of the Invention.
The present invention concerns combustion devices such as internal combustion engines, and more particularly, a system and method for pretreating fuel to achieve so called "hypergolic" combustion, i.e., combustion in which only negligible ignition delay occurs after the fuel comes into contact with oxygen in a combustion chamber and combustion is completed substantially instantaneously.
2. Description of the Prior Art.
It has long been known to preheat fuels in internal combustion engines, as an aid in achieving rapid vaporization and combustion. See for example U.S. Pat. Nos. 4,503,833; 3,765,382; 2,435,213; and 1,262,886.
Such preheating has also been employed for cracking of heavy components in the fuel, as described in U.S. Pat. No. 2,108,706.
Such preheating has in some instances taken the form of a heat exchanger located in the engine exhaust system, as shown in U.S. Pat. No. 3,765,382 and, there is also disclosed in German Pat. No. 451,769, a heat exchanger coil provided in the cylinder head of a piston engine in order to cause preheating of the fuel.
In U.S. Pat. No. 1,262,886 a "retort" is provided in which hot combustion gases are used to heat an incoming quantity of fuel. Such preheating has been limited to moderately high temperatures sufficient only as an aid to rapid vaporization of the fuel and no striking effect on the combustion process by preheating of fuel has been appreciated by those skilled in the art.
There is disclosed in U.S. Pat. No. 4,448,176; SAE paper no. 850089, "Hypergolic Combustion in an Internal Combustion Engine"; and SAE paper no. 820356, "The Influence of Initial Fuel Temperature on Ignition Delay", each of which is hereby incorporated by reference, a concept for reducing ignition delay to negligible values and completion of the combustion process substantially instantaneously after bringing fuel into contact with oxygen containing atmosphere. This is achieved by heating fuel to relatively elevated levels, i.e., to a temperature on the order of 1000.degree. F. Such fuel preheating produces the striking effect of enabling substantially instantaneous ignition and combustion, i.e., "hypergolic" combustion upon bringing the pretreated fuel into contact with an oxidizer.
As disclosed in these references, by preheating fuel to such very high temperature levels, a disproportionate number of fuel molecules are excited to elevated energy states, causing dissassociation of the fuel molecules to produce hydrogen and hydrocarbon radicals. In heating fuel to the 1000.degree. F. range, a critical proportion of fuel molecules are excited, such that it has been found that combustion will be initiated and completed substantially instantaneously upon bringing the preheated fuel into an oxidizing atmosphere, such as compressed air in the combustion chamber of an internal combustion engine. This proportion has been computed theoretically to be approximately 3.times.10.sup.-5 % of the total number of molecules in each quantity of fuel.
As described in the aforementioned references, there are many advantages to the reduction of ignition delay to negligible levels and the achievement of instantaneous combustion, since control over the combustion cycle is thereby enabled.
However, the use of external heat sources for such purpose adversely affects the efficiency of the engine when heating fuel to such highly elevated temperatures. Further, the heat exchanger arrangements heretofore disclosed in the prior art do not enable the degree of heating necessary to accomplish hypergolic combustion.
It is furthermore a general disadvantage of internal combustion engines that an inordinately high proportion of the heat generated is lost, in no small part by conduction through the engine parts forming the combustion chamber.
Accordingly, it is an object of the present invention to provide a regenerative fuel heating system and method for combustion devices, which enables fuel to be heated to elevated levels on the order of 1000.degree. F. such as to enable hypergolic combustion.
It is still another object of the present invention to improve the efficiency of internal combustion engines by reducing the amount of waste heat lost by the engine during operation.